This invention relates to a circular knitting machine for producing tubular elastic netting. Netting of this type has many uses. The preferred embodiment of applicant's invention is used, however, for knitting netting for processing meat such as rump roast, fresh hams and the like. Tubular or circular netting of the type used for the processing of meat products is generally characterized by a plurality of circumferentially spaced warp wales knit from a cotton yarn interconnected by a generally helically disposed elastic weft yarn which is incorporated unknit in spaced chain stitches of the warp wales.
Machines for producing tubular elastic netting of the type just described have been known to the industry for some time. Two such machines which are known to applicant are shown and described in U.S. Pat. No. 3,513,668 to Marcus Mintz and 3,592,024 to Nathan Levin.
Both of the knitting machines shown and described in the Mintz (U.S. Pat. No. 3,513,668) and Levin (U.S. Pat. No. 3,592,024) patents incorporate pivotal warp feed mechanisms which oscillate in a back and forth motion in order to feed a warp yarn to a respective needle. In the patent to Mintz (U.S. Pat. No. 3,513,668) the pivotal warp guides 30 swing from left to right as viewed in FIGS. 7a and 7b. In doing so the warp yarn follows the path indicated in the dotted line of FIG. 7a across the needle and under the hook. As the needle of Mintz is then lowered the warp yarn is drawn down into the needle groove where a warp stitch is made. At this time the cam 34 of Mintz rotates out of engagement with the warp guide 30. The guide 30 is then drawn by the tension in the warp yarn back to its initial position as shown in FIG. 7a prior to making another stitch.
The warp yarn feed mechanism as shown in Levin (U.S. Pat. No. 3,592,024) is quite similar to the Mintz (U.S. Pat. 3,513,668) structure described above. In Levin the warp yarn is fed to its associated needle by means of a generally L-shaped yarn finger 37. The L-shaped yarn finger of Levin is adapted to move in a generally back and forth motion from a first position to a second position under the influence of a plurality of cams 21a, 21b, 21c, 21d (FIG. 2). As a respective cam moves out of engagement with a L-shaped yarn finger such finger returns to its initial position under the influence of a compression spring 39 (FIG. 6).
Applicant has found that there are a number of shortcomings in the operation of the circular knitting machines of the Mintz and Levin designs.
As an example, applicant has found that the spring return mechanism which is required to be associated with each of the L-shaped yarn fingers of the Levin structure is subject to failure from time to time. When a spring fails in a circular knitting machine structure of the type shown in the Levin patent it is necessary to stop the entire machine and replace the spring. The resultant down time not only interrupts production but also necessitates the availability of skilled operators who can attend to the machine at such time as there is a breakdown.
A further disadvantage of the yarn feed machanisms of the type shown in the Mintz or Levin patents discussed above is the fact that the oscillatory or back and forth motion of the yarn feed fingers or guides places a restriction on the number of chain stitches that may be placed in a warp wale with a single rotation of the cam mechanism.
Referring, for example, to FIG. 2 of the Levin U.S. Pat. No. 3,592,024 it will be noted that there are shown and described a total of four cams 21a, 21b, 21c and 21d adapted to rotate about the 20 yarn feed fingers 37. The four cams shown in FIG. 2 of Levin will produce a total of four chain stitches in each warp wale with one complete rotation of the cam mechanism. That is to say, as the four cams shown in FIG. 2 of Levin make a complete rotation about the yarn fingers, each finger will be indexed four times thus to produce a total of four chain stitches in the warp wale associated with each of the fingers. Since the elastic weft wale 17 of Levin rotates with the cams 21a-21d, the apparatus of FIG. 2 of Levin will produce tubular knitting of the type shown in FIG. 7 of Levin with the elastic weft yarn incorporated into the warp wales at every fourth chain stitch. Should it be desired to increase the number of chain stitches in the warp wales between parallel portions of the weft yarn it is necessary to increase the number of cams in the mechanism shown in FIG. 2 of Levin to the number of chain stitches desired. For example, if it is desired to provide that the elastic weft yarn should be incorporated into every six chain stitches of a warp wale, it is necessary to provide for six rotating cams in the mechanism shown in FIG. 2 of Levin in order to index each of the yarn fingers six times during a complete rotation of the cams and weft yarn. Providing extra cams may not be possible, however.
Since the structure shown in FIG. 2 of Levin requires that a certain amount of return time be allowed in order to permit each L-shaped yarn finger to move from its cammed position to its free position, there is a practical limit to the number of cams that can be employed in the Levin structure. If an excessive number of cams are utilized it is not possible for a single yarn finger to complete its oscillation or indexing from its free position to its cammed position (and return) before being indexed by a succeeding cam.
Applicant's improved circular knitting machine eliminates the oscillatory or back and forth motion of the yarn fingers or yarn guides as shown in the Levin and Mintz patents. Rather applicant has incorporated in his circular knitting machine a continuously rotating hollow feed tube which is driven not by cams but rather by an internal ring gear. Applicant has eliminated the necessity of providing spring returns for the yarn feed mechanism thus eliminating the objectionable maintenance problem associated with the repair or replacement of broken springs. In eliminating the oscillation of the ayrn feed mechanism applicant has increased the flexibility of circular knitting machines by making it possible to provide more chain stitches in the warp wale between adjacent portions of the elastic weft yarn.